Latest news is that it might not be. It is currently anchored on the border between Danish territorial waters and the economic exclusion zone with VesselFinder showing it a few meters outside territorial waters. This is important as Denmark isn’t legally allowed to do anything if they aren’t in territorial waters without approval from China.

Officially the Danish navy has denied to comment on whether they have boarded (you can’t really detain a ship at sea), so we’ll probably have to wait to figure out what the situation is, but it is possible to see P525 cruising around the ship. Whatever the case is the next couple of days will for sure be interesting.